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Elijah Newren c91c944a06 rebase: define linearization ordering and enforce it
Ever since commit 3f213981e4 ("add tests for rebasing merged history",
2013-06-06), t3425 has had tests which included the rebasing of merged
history and whose order of applied commits was checked.  Unfortunately,
the tests expected different behavior depending on which backend was in
use.  Implementing these checks was the following four lines (including
the TODO message) which were repeated verbatim three times in t3425:

    #TODO: make order consistent across all flavors of rebase
    test_run_rebase success 'e n o' ''
    test_run_rebase success 'e n o' -m
    test_run_rebase success 'n o e' -i

As part of the effort to reduce differences between the rebase backends
so that users get more uniform behavior, let's define the correct
behavior and modify the different backends so they all get the right
answer.  It turns out that the difference in behavior here is entirely
due to topological sorting; since some backends require topological
sorting (particularly when --rebase-merges is specified), require it for
all modes.  Modify the am and merge backends to implement this.

Performance Considerations:

I was unable to measure any appreciable performance difference with this
change.  Trying to control the run-to-run variation was difficult; I
eventually found a headless beefy box that I could ssh into, which
seemed to help.  Using git.git, I ran the following testcase:
    $ git reset --hard v2.20.0-rc1~2
    $ time git rebase --quiet v2.20.0-rc0~16

I first ran once to warm any disk caches, then ran five subsequent runs
and recorded the times of those five.  I observed the following results
for the average time:

     Before this change:
       "real" timing: 1.340s (standard deviation: 0.040s)
       "user" timing: 1.050s (standard deviation: 0.041s)
       "sys"  timing: 0.270s (standard deviation: 0.011s)
     After  this change:
       "real" timing: 1.327s (standard deviation: 0.065s)
       "user" timing: 1.031s (standard deviation: 0.061s)
       "sys"  timing: 0.280s (standard deviation: 0.014s)

Measurements aside, I would expect the timing for walking revisions to
be dwarfed by the work involved in creating and applying patches, so
this isn't too surprising.  Further, while somewhat counter-intuitive,
it is possible that turning on topological sorting is actually a
performance improvement: by way of comparison, turning on --topo-order
made fast-export faster (see
https://public-inbox.org/git/20090211135640.GA19600@coredump.intra.peff.net/).

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-12-28 12:49:48 -08:00

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#!/bin/sh
test_description='rebase topology tests with merges'
. ./test-lib.sh
. "$TEST_DIRECTORY"/lib-rebase.sh
test_revision_subjects () {
expected="$1"
shift
set -- $(git log --format=%s --no-walk=unsorted "$@")
test "$expected" = "$*"
}
# a---b-----------c
# \ \
# d-------e \
# \ \ \
# n---o---w---v
# \
# z
test_expect_success 'setup of non-linear-history' '
test_commit a &&
test_commit b &&
test_commit c &&
git checkout b &&
test_commit d &&
test_commit e &&
git checkout c &&
test_commit g &&
revert h g &&
git checkout d &&
cherry_pick gp g &&
test_commit i &&
git checkout b &&
test_commit f &&
git checkout d &&
test_commit n &&
test_commit o &&
test_merge w e &&
test_merge v c &&
git checkout o &&
test_commit z
'
test_run_rebase () {
result=$1
shift
test_expect_$result "rebase $* after merge from upstream" "
reset_rebase &&
git rebase $* e w &&
test_cmp_rev e HEAD~2 &&
test_linear_range 'n o' e..
"
}
test_run_rebase success ''
test_run_rebase success -m
test_run_rebase success -i
test_run_rebase () {
result=$1
shift
expected=$1
shift
test_expect_$result "rebase $* of non-linear history is linearized in place" "
reset_rebase &&
git rebase $* d w &&
test_cmp_rev d HEAD~3 &&
test_linear_range "\'"$expected"\'" d..
"
}
test_run_rebase success 'n o e' ''
test_run_rebase success 'n o e' -m
test_run_rebase success 'n o e' -i
test_run_rebase () {
result=$1
shift
expected=$1
shift
test_expect_$result "rebase $* of non-linear history is linearized upstream" "
reset_rebase &&
git rebase $* c w &&
test_cmp_rev c HEAD~4 &&
test_linear_range "\'"$expected"\'" c..
"
}
test_run_rebase success 'd n o e' ''
test_run_rebase success 'd n o e' -m
test_run_rebase success 'd n o e' -i
test_run_rebase () {
result=$1
shift
expected=$1
shift
test_expect_$result "rebase $* of non-linear history with merges after upstream merge is linearized" "
reset_rebase &&
git rebase $* c v &&
test_cmp_rev c HEAD~4 &&
test_linear_range "\'"$expected"\'" c..
"
}
test_run_rebase success 'd n o e' ''
test_run_rebase success 'd n o e' -m
test_run_rebase success 'd n o e' -i
if ! test_have_prereq REBASE_P; then
skip_all='skipping git rebase -p tests, as asked for'
test_done
fi
test_expect_success "rebase -p is no-op in non-linear history" "
reset_rebase &&
git rebase -p d w &&
test_cmp_rev w HEAD
"
test_expect_success "rebase -p is no-op when base inside second parent" "
reset_rebase &&
git rebase -p e w &&
test_cmp_rev w HEAD
"
test_expect_failure "rebase -p --root on non-linear history is a no-op" "
reset_rebase &&
git rebase -p --root w &&
test_cmp_rev w HEAD
"
test_expect_success "rebase -p re-creates merge from side branch" "
reset_rebase &&
git rebase -p z w &&
test_cmp_rev z HEAD^ &&
test_cmp_rev w^2 HEAD^2
"
test_expect_success "rebase -p re-creates internal merge" "
reset_rebase &&
git rebase -p c w &&
test_cmp_rev c HEAD~4 &&
test_cmp_rev HEAD^2^ HEAD~3 &&
test_revision_subjects 'd n e o w' HEAD~3 HEAD~2 HEAD^2 HEAD^ HEAD
"
test_expect_success "rebase -p can re-create two branches on onto" "
reset_rebase &&
git rebase -p --onto c d w &&
test_cmp_rev c HEAD~3 &&
test_cmp_rev c HEAD^2^ &&
test_revision_subjects 'n e o w' HEAD~2 HEAD^2 HEAD^ HEAD
"
# f
# /
# a---b---c---g---h
# \
# d---gp--i
# \ \
# e-------u
#
# gp = cherry-picked g
# h = reverted g
test_expect_success 'setup of non-linear-history for patch-equivalence tests' '
git checkout e &&
test_merge u i
'
test_expect_success "rebase -p re-creates history around dropped commit matching upstream" "
reset_rebase &&
git rebase -p h u &&
test_cmp_rev h HEAD~3 &&
test_cmp_rev HEAD^2^ HEAD~2 &&
test_revision_subjects 'd i e u' HEAD~2 HEAD^2 HEAD^ HEAD
"
test_expect_success "rebase -p --onto in merged history drops patches in upstream" "
reset_rebase &&
git rebase -p --onto f h u &&
test_cmp_rev f HEAD~3 &&
test_cmp_rev HEAD^2^ HEAD~2 &&
test_revision_subjects 'd i e u' HEAD~2 HEAD^2 HEAD^ HEAD
"
test_expect_success "rebase -p --onto in merged history does not drop patches in onto" "
reset_rebase &&
git rebase -p --onto h f u &&
test_cmp_rev h HEAD~3 &&
test_cmp_rev HEAD^2~2 HEAD~2 &&
test_revision_subjects 'd gp i e u' HEAD~2 HEAD^2^ HEAD^2 HEAD^ HEAD
"
# a---b---c---g---h
# \
# d---gp--s
# \ \ /
# \ X
# \ / \
# e---t
#
# gp = cherry-picked g
# h = reverted g
test_expect_success 'setup of non-linear-history for dropping whole side' '
git checkout gp &&
test_merge s e &&
git checkout e &&
test_merge t gp
'
test_expect_failure "rebase -p drops merge commit when entire first-parent side is dropped" "
reset_rebase &&
git rebase -p h s &&
test_cmp_rev h HEAD~2 &&
test_linear_range 'd e' h..
"
test_expect_success "rebase -p drops merge commit when entire second-parent side is dropped" "
reset_rebase &&
git rebase -p h t &&
test_cmp_rev h HEAD~2 &&
test_linear_range 'd e' h..
"
# a---b---c
# \
# d---e
# \ \
# n---r
# \
# o
#
# r = tree-same with n
test_expect_success 'setup of non-linear-history for empty commits' '
git checkout n &&
git merge --no-commit e &&
git reset n . &&
git commit -m r &&
git reset --hard &&
git clean -f &&
git tag r
'
test_expect_success "rebase -p re-creates empty internal merge commit" "
reset_rebase &&
git rebase -p c r &&
test_cmp_rev c HEAD~3 &&
test_cmp_rev HEAD^2^ HEAD~2 &&
test_revision_subjects 'd e n r' HEAD~2 HEAD^2 HEAD^ HEAD
"
test_expect_success "rebase -p re-creates empty merge commit" "
reset_rebase &&
git rebase -p o r &&
test_cmp_rev e HEAD^2 &&
test_cmp_rev o HEAD^ &&
test_revision_subjects 'r' HEAD
"
test_done